I use the app about half the time, and the website the other half. Each has advantages! For example, the app lets you search for a food in your history for a type of meal, but the website lets you scroll through a history for all meals (I wish both did both). They handle negative entries differently as well (the app doesnt let you enter a minus). But I think its pretty darn useful for a free app, especially considering the database of user-entered foods you get access to!
stephannm about MyFitnessPal: Calorie Counter